it is made up of different materials most of it is iron and copper
A flywheel is made basically like a brake rotor, and the clutch disc is made like brake pads. The spinning flywheel is pressed against the clutch disc, which is made of hard steel--the idea being to get the clutch side of the trans to spin.
A clutch is a disc usually made of metal, with a hub, spokes, and sometimes springs. Some clutches are cone shaped.
hydraulic single disc clutch
clutch pedal free play decreases
If the disc is installed correctly the clutch will engage and disengage smoothly. In most cases if the disc is installed backwards the clutch disc will bind against the flywheel/crankshaft bolts and not release resulting with a clutch that doesn't disengage. More than likely if the disc was installed backwards the disc is now damaged and will need to be replaced.
You replace it. The oil is in the clutch face and if you use it, the face will come off of the disc. There is no way to clean it.
no adjustment on hydraulic clutch, worn clutch disc and pressure plate
Clutch disc is worn out. Not knowing what vehicle you have, most are hydraulically operated and there is no adjustment. Time for clutch replacement.
Between the two clutch facings
Clutch disc, pressure plate, transmission shaft,
If it has a hydraulic clutch, I believe they can not be adjusted. When the pedal travel is no longer acceptable the clutch disc must be replaced.
There are various reasons why an oil leak can penetrate a clutch disc. There could possibly be a rear main seal failure. Another possibility could be a failure of the main input shaft seal which could leak towards the clutch disc.